Operating at or near the transmission operating temperature (e.g., approximately 90-100° C.) can have a notable impact on fuel economy of the vehicle, such as during driving scenarios similar to the FTP emissions test cycle. During such driving scenarios, the automatic transmission fluid (ATF) temperature typically does not approach operating temperature, which reduces transmission efficiency and lowers fuel economy. Some systems have been proposed to heat the ATF with engine coolant waste heat or with electric heaters, to thereby provide additional heating to the ATF and more quickly achieve the operating temperature. However, such systems may be complicated and expensive. Accordingly, while such systems work for their intended purpose, it is desirable to provide improved supplemental ATF heating in an automatic transmission.